The core logic for determining the preload of a hot runner sensor is: first, determine the standard range based on the installation structure; then, through machining dimension allowance and secondary control of assembly operations; and finally, confirm by verifying the contact force. The specific method is as follows:
1. First, determine the standard range of the preload based on the installation structure. The core acceptable range for the preload is 0.1~0.3mm. Fine-tuning can be applied according to different installation structures and usage scenarios. Specific standards are:
|
Installation Structure/Scenario |
Preload Standard Range |
Corresponding Acceptable Contact Force Range |
|
Threaded Clamping Type (Most Commonly Used) |
0.15~0.25mm |
8~12N |
|
Set Screw Fixed Type |
0.1~0.2mm |
5~10N |
|
Large Mold High-Pressure Molding Scenarios |
0.2~0.3mm |
10~15N |
2. The preload is determined through dimensional calculations during the machining stage.
The preload is directly determined by the machining dimensions and can be accurately calculated before machining:
First, measure the probe protrusion length of the actual sensor: that is, the distance from the sensor probe end face to the sensor mounting thread end face.
Determine the required mounting hole depth: the actual depth from the mold mounting surface to the bottom of the hole. The calculation formula is:
Mounting hole depth = Probe protrusion length - Target preload
During machining, strictly control the hole depth tolerance within ±0.05mm. After machining, remeasure the hole depth to confirm that the preload meets the standard range for the corresponding structure.
3. Preload Determination During Assembly Control
If the hole depth has already been machined, the preload can be indirectly determined by the number of turns tightened during assembly, without the need for specialized instruments:
Threaded Clamping Type: First, manually tighten the sensor to its position (probe to the bottom of the hole), then tighten an additional 1/12 to 1/6 turn to obtain a preload of 0.1 to 0.3 mm, matching a qualified contact force of 5 to 15 N.
Set Screw Fixed Type: First, press the sensor firmly against the bottom of the hole, tighten the set screw until it stops, then tighten an additional 1/8 to 1/4 turn to meet the corresponding preload standard.
If using a torque wrench, the preload can be directly matched by torque: M3 thread torque 0.3 to 0.6 N·m, M4 torque 0.5 to 1.0 N·m, corresponding to preload and contact force within the qualified range.
4. Verify and confirm the preload amount is qualified.
After determining the preload amount, verification is required to confirm that it meets the requirements:
Precise verification: After assembly, use a digital push-pull force gauge to test the contact force. Repeat 3 times and take the average value. If the corresponding contact force falls within the range of 5~15N, it indicates that the preload amount is qualified.
Rapid on-site verification: Observe the temperature measurement performance. If the difference between the heating rate and that of a qualified sensor of the same specification is <30%, and the stable production temperature fluctuation is ≤±3℃, it indicates that the preload amount is appropriate.
